Strain relief fittings for electrical cords provide a means for restraining longitudinal motion of the cord, with respect to the strain relief fitting, in response to a longitudinal force on the cord. A usual object is to prevent any strain from being transmitted to the electrical connection. Such devices are widely used on appliances and in other applications wherein an electrical cord passes through a panel or wall. One of the simplest forms of strain relief devices comprises tying a knot in the wire to form an enlarged portion which is too large to pass through a hole in the wall. Other simple forms include a post around which a wire is tied; a girdle compressively encircling the cord and attached by some convenient means to the panel; and a wedging device to preclude longitudinal motion of the electrical cord. Other simple devices have been employed which apply encircling pressure and/or puts one or more sharp bends in the wire to restrain the wire from longitudinal motion. Each of these techniques, and a wide variety of other techniques, have served admirably in particular types of applications. Other varieties of strain relief devices have been developed for specialized applications and/or to accommodate a wide variety of types and sizes of electrical cords. Each type has its advantages and limitations. Some provide inadequate holding force; others pierce or otherwise damage the wire; some fail to provide a liquid tight seal; others are too expensive.
Strain relief devices have been combined with liquid tight techniques for preventing the transmission of moisture from one side of a panel or wall to the other. When liquid tight seals are desired, it has been conventional to provide a rubber or elastomeric sleeve which has a hole therethrough with slightly slanted sides through which the electrical cord is passed. Subsequently, a body member enclosing the sealing sleeve provides a compressive force which causes the sleeve to engage the electrical cord to provide a liquid tight seal. In some prior art structures, a liquid tight seal of the type described is combined with a gripping member which is somewhat analogous to the jaws of a drill chuck in that the gripping member includes a plurality of fingers which are cammed to be deflected angularly inward in response to the assembly of a body around it.
These prior art forms of strain relief devices have a variety of disadvantages. For example, some require an excessive number of parts which may be difficult and/or inconvenient to assemble. In many cases, a given structure works only with a very limited range of cable sizes. Some have a tendency to rupture the cable sheath or inflict other damage on the cable. Some fail to provide sufficient pull out resistance. Some prior art devices tend to lose effectiveness in time and/or when exposed to certain environments such as some chemical atmospheres and/or wide temperature and/or humidity ranges.